Safety-plug.



No. 848,205. l l PATENTED MAR. 26, 1907.

B. W. ROBINSON.

. SAFETY PLUG.

APPLICATION FILED JAN. 5, 1907.

' which wil BLISS W. ROBINSON, OF BOSTON, MASSACHUSETTS.

SAFETY-PLUG.

Specification of Letters Patent.

Patented March 26, 1907.

Application filed January 5, 1907. Serial No. 350,887.

To @ZZ wil/0m, t may concern: f

' Beit known that I, BLiss W. ROBINSON, a

citizen of the United States, residing in Boston, county of Sufl'olk,and State of Massachusetts, have invented an Improvement inSafety-Plugs, of which the following description, in connection with-theaccompanying drawing, is a specification, like letters on the drawingrepresenting like parts.

This invention relates to safety-plugs, such as are commonly uscd intubular or fire-tube boilers for givingindication when the water in theboiler drops below a predetermined level. i

The common form of safety-plug is a cylindrical or tubular member whichis filled with some suitable fusible material and which is screwed intothe flue-sheet of the boiler just below the normal water-level. Usuallythe bore of the safety-'plug is tapering, it being larger at its innerend than at its outer end. While plugs of this nature answer the purposewhere the steam-pressure in the boiler is comparatively low, yet it hasbeen found that where the boiler-pressure is comparatively high it willgradually force the Afusible metal out through the outer end-of the plugeven while the inner end of the plug is still covered with water. This`is so because the fusible metal often becomes slightly softened, owingto the extreme heat to which the fluesheet is subjected, and when thefusible metal does thus soften slightly the pressure on the inner end ofthe plug is sufiicient to force some of the metal out through the plug.When this occurs, the plug is unfit for further use.

The principal object of my present invention is to rovide a novel formof safety-plug Pretain the fusible metal under any degree of pressure.

Another object of the invention is to rovide a plug in which the fusiblemetal wi be protected better. than in plugs as usually made.

Someiembodiirnents of my invention will be describen vand then the novelfeatures thereof will be pointed out in the claims.

In the drawings,-Figure 1 shows a ortion of a tubularfboiler having asafety-p ug applied thereto. Fig. 2 is a section through a safetylug ofthe ordinary type, showing how it is a ected byeXtremely-highpressures.

Fig. 3 is a section through a safety-plug of one form embodying myinvention. Fig. 4 is a section on the line :c Fig. 3. Fig. 5 is a sideview of one end of the plug. Fig. 6 is an end view thereof with thefusible metal omitted. Fig. 7 is a sectional view showing anotherembodiment of my invention. F'g. 8 is a section on the line y y, Fig. 7.Fig. 9 is an end view of Fig. 7 with the fusible metal omitted.

I have not shown herein a complete boiler, but only a sufficient portionthereof to illustrate my invention, and in Fig. l, 3 designates theboiler-shell, 4 a flue-sheet therein,

and 5 the flues through which the products of combustion pass. Inboilers of this type it is customary to place one or more safety-plugsin the flue-sheet t above the flues 5, so that when the water-leveldrops the safety-plug will be uncovered before any of the flues.

A safety-plug of the usual forni is shown in v Fig. 2, and it comprisesa bushing member or shell 6, having a tapering bore therethrough filledwith fusible metal 7. When a'plug of this form is used ina boilercarrying very high pressure, the heat to which the plug is subjected isoften enough to soften the fusible metal sufficiently so that` theeXtreinelyhigh pressure within the boiler will force the metal outthrough the plug, as shown in dotted lines, Fig. 2, even though theinner end of the plug is below the water-le vel. When this occurs, theplug is practically useless and a new plug has to be inserted.

My improved safety-plug is provided with the usual screw-threadedportion 8, which is screwed into the flue-sheet 4 and is alsoprovidedwith a central bore 13, extending therethrough, and in order to producea plug in which the fusible materia.l will be retained regardless of thepressure in the boiler I make my plug with a resistance member which issituated to cover, and thus take the pressure from a portion of, thefusible material at the inner end of the plug.A In the presentembodiment of my invention this member is in the form of an inner wall9, which is situated IOC within the bore 13 at Athe inner end of thetion 14 of the inner walls 9 takes the around the fins and extends intothe bore 13 as far as desired. The metal forming the inner walls 9closes or substantially closes the end of the chamber iiiclosed by saidwalls, as indicated at 14. The outer walls 10 may, if desired7 have oneor more 'a ertures or erforations therein, into W 'oh the fusible metalextends, the metal which enters'said apertures serving to anchor thebody of fusible metal'in place. With this construction it will be 'seenthat the area of fusiblel metal on which the steam-pressure in theboiler is exerted is simply that of the annular space between the walls9 and 1() and that the porressure on the'center of the plug. With t `sconstruction the pressure on the fusible metal will not be sufficient tocause the lmetal to flow out through the bore 13 even if the pressure inthe boiler is an extremely-high one, because this steain-pressure islargely taken by the inner `wall 9 and only a portion of it ycomesdirectly on the fusible metal.' Furthermore, the presence of the fins 11act to hold the metal in lace and prevent it from being forced out tough the bore 13. The

number of fins 11 employed the pil/ug is not essential to the invention.

In practice I prefer to place one of the apertures 15 on the under sideof the plug, so

that when the water-level-drops below the plug and the plug blows themelted fusible metal willrun out fof the lower a erture 15 as well asbeing blown through the ore 13.

In Figs. 7, 8, and 9 I have shown a plug of a littledifferentconstruction-that is, one havin only two webs or fins 11, whichconnect tie inner and outer walls. .In this form of the invention theslots or apertures 15a extend clear through to the inner end. of theplug. In other respects, however, the plug shown in Figs. 7, 8, and 9 issimilarlto that shown in Figs. 3, 4, and 5. If desired, the

' portion 14 of the wall may be provided with an aperture 16, althoughthis is not essential. i

-From the'above it will be seen thatla plug embodying my invention hassuch a construction that the metal will not be-forced out through thebore 13 even when subjected to extremely-hi h pressure, thefshape of theplug being suc as to relieve the Vfusible metal largely from thepressure within the boiler. 1

The shape herein shown for the protecting or resistance 'member 9 is notessential to my invention, although I prefer the form shown, because itforms within it a waterchamber that serves to give added protection tothe fusible metal.

Upon reigning to uw drawings it Wiii be seen that the water not onlysurrounds. the

plug, but also fills the chfamber formed therein, and thus a much reaterarea is exposed to the water than wit i the ordinary type of plug. Theresult of this construction is that the fusible metal will not melt orbecome sufficiently softened tov run so long water covers the end of theplug When, however, the water drops below the level of the plug, the.fusible metal will fuse very quickly, because it is largely situated inan annular space. A plug having this con-l struction is therefore a verysensitive one as well as one which will withstand considerable pressure.A

Ilaviiig described my invcntion, what I 'claim as new, and desire tosecure by Letters Patent, is

1. A safety-plug com rising a body of nonfusible material provi( cd witha bore containing fusible material, and means to cover a portion only ofthe fusible material at the inner end of the plug.

2. A safety-plug com rising a body of nonfusible material provi ed witha bore containing fusible material, and means within the bore to cover aportion onlyof the fusible material. y

3. 'A safety-plug having a bore containing fusible material, and amember forming an integral part of the plug and situated within th'e:bore to cover a portion ofthe fusible material.

` 4. A safety-plug having at one end longitudinally-extending inner andouter walls s aced from each other, and fusible material ling the/spacebetween said walls.

5. A safety-plug having at one end longitudinally-extending inner andouter walls spaced from each other, and fusiblev material fillingthe sace between said walls, the space surrounds by the inner wallconstituting a water-space.

6. A safety-plu'ghaving at one end annular inner and outer walls rigidlyconnected together by ns, and fusible material filling the space betweensaid walls.

as the A ICO l 7. A safety-plug having at one end an inner andan outerwall spaced from each-other, and fusible material filling the sp acebetween said walls, said outer wall being perforated'.

iro

8. A'safety-plug having a bore containin(T fusible material and providedat with a water-chamber.

9:k A safety-plug having a bore Ioo ntainin fusible material andprovided at its inner en( with an axially-extending water-chamber.

10. A safety-plug com rising an outer exteriorly screw threade memberprovided with a bore, an inner annular resistance-w all 9 at the innerend of the member 8 and forming with said inner member an annular space,and fusible materialqiilling said. annular spa e c 11 A safety-plugcomprising an annular 'ts inner end seeoe s l exteriorly -sorewthreadedmember 8 proname to this specification in the presence of .E vided witha central bore and having en antwo subscribing Witnesses.

nular resistance-Wall 9 Within the bore at the inner end thereof and`connected to the mem- B W' ROBINSON' 5 ber 8 by ins l1, and fusiblematerial filling Witnesses:

the bore around the resistance-Wall 9. ['LOUIS C. SMITH,

In testimony whereof I have signed my 'EVANGELINE C. BROWN.

